The frog here is one of five you have to gather with the Don Gero mask.

On the second day, the music man is here, kicked out of the inn. Talk to him as Kafei to learn about his time with the Bremen band, and to get the Bremen mask. This will let animals march after you - great for little chickens!

On the second day, you also see Anju's letter delivered to Kafei at 3pm, if you've done the meeting with Anju. You then can talk to Kafei and learn about the mask thief. When you return at 1pm on Day 3, you learn that Kafei has gone off to catch the thief in the mountains. You get a package to deliver to the Mayor's Wife.
Majora's Mask Walkthrough Page